Nucleic acid levels, cellular activity and growth during the puerulus stage of the Western Rock Lobster (Panulirus cygnus (George); Decapoda: Palinuridae)

The potential impact of non-feeding in pueruli of the Western Rock Lobster Panulirus cygnus (George; Decapoda, Palinuridae) on cellular activity and growth was investigated through fluorometric quantification of nucleic acid levels. Late phyllosomata, post-settlement pueruli and juveniles were collected along the Western Australian coast between August and December 1992, by means of plankton nets and puerulus collectors. Early phyllosomata were obtained through laboratory rearing. Nucleic acid levels, as well as dry weights (DW), increased gradually during early phyllosomal stages; the RNA/DNA ratio remained fairly constant between 0.3 and 0.5 units. During puerulus development, DNA levels (a measure for cellular growth) demonstrated a slight but insignificant increase; DW remained fairly constant. However, after ecdysis to the first juvenile stage, DNA levels were significantly higher (similar to 0.93 mg DNA . individual(-1)), compared with early post-settlement pueruli (similar to 0.35 mg DNA . ind(-1)), and increased further during juvenile development (similar to 1.08 mg DNA . ind.(-1) in the second moult juvenile). DW of the second juvenile stage (142.5 mg) was approximately double that of the puerulus. RNA levels demonstrated a slight but insignificant decrease during puerulus development, and an increasing trend during juvenile development. RNA/DNA ratios (an indicator for cellular activity) are high in the final phyllosoma (1.17 +/- 0.13 units), and decrease significantly during the puerulus stage (to 0.49 +/- 0.05 units in the early post-settlement puerulus) and first moult juveniles (0.26 +/- 0.13 units), and only demonstrates a slight but insignificant recovery after the second moult juveniles (0.45 +/- 0.07 units). Water temperature appears to have an important impact on RNA levels, which approach zero immediately after ecdysis to the first juvenile stage when post-settlement pueruli were maintained at 23 degrees C; those maintained at 18 degrees C did not demonstrate a significant decrease. These observations are consistent with absence of feeding during the puerulus stage and further suggest that water temperature may have a substantial effect on puerulus development.